1. Field of the Invention
The present invention pertains to a radiation detector, a radiographic image capturing system, a radiation detection method, and a radiation detection program storage medium and particularly relates to a radiation detector, a radiographic image capturing system, a radiation detection method, and a radiation detection program storage medium that capture a radiographic image without having to synchronize with a radiation application action of a radiation applicator.
2. Description of the Related Art
Conventionally, radiographic image capturing systems that perform radiographic imaging for the purpose of medical diagnoses have been known. As one such radiographic image capturing system, there is a radiographic image capturing system that is equipped with a radiation applicator that applies radiation, a radiation detector—such as what is known as a cassette—that detects the radiation that has passed through a subject to capture a radiographic image, and a controller that controls the radiation applicator and the radiation detector.
In recent years, there have been radiation detectors using a flat panel detector (FPD) that is capable of converting the detected radiation into electrical signals. Because dark current, which contributes to noise, exists in a two-dimensional solid-state imaging device such as an FPD, the imaging time of the solid-state imaging device cannot be lengthened unreasonably. For this reason, synchronization of the application action, in which the radiation detector transmits signals to and receives signals from the radiation applicator and in which the radiation applicator applies the radiation, and the imaging action, in which the FPD performs imaging (performs detection of the radiation), is performed.
Specifically, with respect to an imaging request signal from the radiation applicator, the FPD performs initialization of the solid-state imaging device and, after the initialization has been completed, transmits an imaging preparation completion signal to the radiation applicator. After the radiation applicator receives the imaging preparation completion signal, the radiation applicator starts the application of the radiation, ends the application of the radiation after a preset application time has elapsed, and transmits an application end signal to the FPD. When the FPD receives the application end signal, the FPD ends a charge storage action by the solid-state imaging device and transitions to an output action in which the FPD outputs image data of the detected radiographic image to the controller.
In such cases as this, since the radiation applicator is hand-operated in order to control the FPD, the interface for an operator becomes complex and it is necessary to configure the radiation applicator and the FPD as a single integrated system. This leads to an increase in the size and an increase in the complexity of the device.
As a radiation detector that addresses such problems, there is a radiation detector in which the radiographic image is detected by the radiation detector without having to connect to the radiation applicator and without having to transmit signals to and receive signals from the radiation applicator (without having to synchronize with the radiation applicator). For example, Japanese Patent Application Laid-Open (JP-A) Nos. 2005-13272 and 2003-307569 disclose technologies in which the timing of the application of the radiation is determined by the FPD.
As a technology for determining the timing of the application of the radiation that is applied from the radiation applicator in order for the radiation detector to capture a radiographic image of a subject, there is a technology of determining it is the application timing in a case in which charge information (QL value) that has been read out from the solid-state imaging device has reached a predetermined threshold value or greater.
However, the characteristics of the solid-state imaging device of the radiation detector may change in response to temperature. Therefore, the QL value may change due to changes in temperature even if the exposure amount of the radiation detector due to the dose of the radiation applied from the radiation applicator does not change. In such cases, the precision with which the radiation detector detects the radiation drops.